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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Korean Journal of Optics and Photonics
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Journal DOI :
Optical Society of Korea
Editor in Chief :
Volume & Issues
Volume 19, Issue 6 - Dec 2008
Volume 19, Issue 5 - Oct 2008
Volume 19, Issue 4 - Aug 2008
Volume 19, Issue 3 - Jun 2008
Volume 19, Issue 2 - Apr 2008
Volume 19, Issue 1 - Feb 2008
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The Improvement of the Correlation Method for Shack-Hartmann Wavefront Sensors using Multi-Resolution Method
Yoo, Jae-Eun ; Youn, Sung-Kie ;
Korean Journal of Optics and Photonics, volume 19, issue 1, 2008, Pages 1~8
DOI : 10.3807/HKH.2008.19.1.001
Shack-Hartmann sensors are widely employed as a wavefront measuring device in various applications. Adaptive optics is one of the major applications. Since an adaptive optics system should be operated in real-time, high-speed wavefront sensing is essential. In high-speed operation, integration time of an image detector is very short. In this case, noises such as readout noise and photon noise greatly influence the accuracy of wavefront sensing. Therefore a fast and noise-insensitive centroid finding algorithm is required for the real-time wavefront sensing. In this paper, the multi-resolution correlation method is proposed. By employing multi-resolution images, this method greatly reduces the computation time when compared to the fast Fourier transform (FFT) correlation method. The verification is performed through the computational simulation. In this paper, the center of mass method, correlation method and multi-resolution correlation method are employed to compare the measurement accuracy of the centroid finding algorithms. The accuracy of a Shack-Hartmann wavefront sensor using the proposed algorithm is proved to be comparable to that of the conventional correlation method.
A New Type of Yagi-Uda Antenna for High Terahertz Output Power
Han, Kyung-Ho ; Park, Yong-Bae ; Kim, Sang-In ; Park, Ik-Mo ; Lim, Han-Jo ; Han, Hae-Wook ;
Korean Journal of Optics and Photonics, volume 19, issue 1, 2008, Pages 9~14
DOI : 10.3807/HKH.2008.19.1.009
In this paper, a new type of Yagi-Uda antenna that operates in the terahertz frequencies is designed. The proposed Yagi-Uda antenna can obtain high input resistance of approximately
at the resonance frequency by using a full-wavelength dipole instead of a half-wavelength dipole as the driver element. The current leakage into the bias line was minimized by applying the photonic bandgap structure to the bias line. By designing the antenna on a thin substrate, the impedance lowering of an antenna caused by the relative dielectric constant of the substrate was prevented and the end-fire radiation pattern which is the original radiation characteristic of the Yagi-Uda antenna could be obtained. We expect that the proposed Yagi-Uda antenna can achieve increased terahertz output power by improving the impedance mismatching problem with the photomixer.
Fiber-Optic Inteferometric Voltage Sensor using a Hollow Fiber
Bae, Jeung-Hwan ; Park, Jae-Hee ; Kim, Kyung-Chan ; Kim, Kwang-Taek ; Han, Won-Taek ;
Korean Journal of Optics and Photonics, volume 19, issue 1, 2008, Pages 15~19
DOI : 10.3807/HKH.2008.19.1.015
A fiber-optic interferometric voltage sensor with high sensitivity is investigated. The fiber-optic voltage sensor is composed of an In-Line Michaelson interferometer bonded on a PZT. The In-Line Michaelson interferometer is a hollow optical fiber spliced to a single-mode fiber at one end and cleaved at the other end. The phase shift of the sensor output signal was induced by the applied AC voltage. The relation between the amplitude of the applied voltage and the phase shift of the sensor output signal was approximately linear and the sensitivity was
Color Filter Based on a Sub-Wavelength Patterned Poly-Silicon Grating Fabricated using Laser Interference Lithography
Yoon, Yeo-Taek ; Lee, Hong-Shik ; Lee, Sang-Shin ; Kim, Sang-Hoon ; Park, Joo-Do ; Lee, Ki-Dong ;
Korean Journal of Optics and Photonics, volume 19, issue 1, 2008, Pages 20~24
DOI : 10.3807/HKH.2008.19.1.020
A color filter was proposed and demonstrated by incorporating a subwavelength patterned 1-dimensional grating in poly silicon. It was produced by employing the laser interference lithography method, providing much wider effective area compared to the conventional e-beam lithography. A
layer was introduced on top of the silicon grating layer as a mask for the etching of the silicon, facilitating the etching of the silicon layer. It was theoretically found that the selectivity of the filter was also improved thanks to the oxide layer. The parameters for the designed device include the grating pitch of 450 nm, the grating height of 100 nm and the oxide-layer height of 200 nm. As for the fabricated filter, the spectral pass band corresponded to the blue color centered at 470 nm and the peak transmission was about 40%. Within the effective area of
, the variation in the relative transmission efficiency and in the center wavelength was less than 10% and 2 nm respectively. Finally, the influence of the angle of the incident beam upon the transfer characteristics of the device was investigated in terms of the rate of the relative transmission efficiency, which was found to be equivalent to 1.5%/degree.
Device Miniaturization using Butterfly Grating-Assisted MMI Couplers
Ho, Kwang-Chun ;
Korean Journal of Optics and Photonics, volume 19, issue 1, 2008, Pages 25~30
DOI : 10.3807/HKH.2008.19.1.025
In this paper, a novel architecture for device miniaturization of multimode interference-based (MMI) couplers is proposed. The coupling length of
MMI couplers scales as the square of the MMI region width so that the use of these structures with large-N ports can require large chip size. To solve the design problem, the butterfly grating-assisted MMI couplers, that have smaller device dimensions than conventional MMI couplers, are discussed and evaluated. Numerical simulations and novel design rules for such structures derived through theoretical analysis are presented.
Design of a Rod-Type Aspheric Lens Collimator for Optical Telecommunication
Kang, Seok-Bong ; Kang, Eun-Kyoung ; HwangBo, Chang-Kwon ; Kang, Sang-Do ; Kim, Jong-Sup ;
Korean Journal of Optics and Photonics, volume 19, issue 1, 2008, Pages 31~35
DOI : 10.3807/HKH.2008.19.1.031
A rod-type aspheric lens collimator for the optical telecommunication system which shows high coupling efficiency and experiences small coupling loss for misalignment errors is designed. The working distance, thickness, and diameter of the rod-type aspheric lens are determined to be close to those of the GRIN lens collimator in order to replace the GRIN lens with the rod-type aspheric lens. Since the coupling loss mainly originated from the spherical aberration of the lens, the spherical aberration in the rod-type aspheric lens is reduced drastically, and it turns out that the coupling efficiency of the rod-type aspheric lens collimator is higher than that of the available collimators, such as ball lens, GRIN lens, and C-type lens collimators.
Measurement of Hysteresis in PZT-Type Tunable Filters Utilizing OFDR
Park, Do-Hyun ; Yeh, Yun-Hae ;
Korean Journal of Optics and Photonics, volume 19, issue 1, 2008, Pages 36~42
DOI : 10.3807/HKH.2008.19.1.036
Implementation of a wavelength-swept source with constant tuning rate adopting a PZT-type tunable filter, requires the knowledge of hysteresis of the filter used. The hysteresis must be considered to avoid any degradation in resolution of the optical frequency domain reflectometry (OFDR) system. An optical spectrum analyzer (OSA) could be used to do the hysteresis measurement, but its measurement time is too long for the high-speed driving conditions for the filter. We proposed a new hysteresis measurement method based on OFDR, which could measure the hysteresis in a real driving condition. A hysteresis measurement apparatus consisted of wavelength-swept source, interferometer, signal processing unit, and PC program is built and used to do the measurement. It is concluded that the new method is useful in the measurement of hysteresis at real driving conditions by successfully implementing a swept-wavelength source whose wavelength change is linear in time.
LGP Output Characteristics Depending in BLU Pattern Size
Kim, Young-Chul ;
Korean Journal of Optics and Photonics, volume 19, issue 1, 2008, Pages 43~47
DOI : 10.3807/HKH.2008.19.1.043
Nowadays, the pattern size of BLU (Back Light Unit) adopted in TFT-LCD (Thin Film Transistor Liquid Crystal Display) is typically a few tens of micrometers. However, recently, researches on the TFT-LCD output characteristics depending on various types of BLU patterns are being performed in order to improve the output and uniformity. In this study, we analyzed the influence of pattern size, distribution, and areal ratio on the output characteristics.
An Optical Configuration for the Normally Black Twisted Nematic Liquid Crystal Cell
Kim, Ki-Han ; Baek, Jong-In ; Kim, Jae-Chang ; Yoon, Tae-Hoon ;
Korean Journal of Optics and Photonics, volume 19, issue 1, 2008, Pages 48~53
DOI : 10.3807/HKH.2008.19.1.048
We propose an optical configuration to compensate dispersion characteristics in the dark state of normally black twisted nematic (NB-TN) liquid crystal display (LCD). We employed a half-wave plate (HWP) and a +A plate to achieve the superior dark state. By using the parameter space diagram (PSD) method, we could obtain the optimum values of parameters and the high contrast-ratio over 500 : 1 could be obtained. Furthermore, excellent dispersion characteristics were also obtained in the bright state. We could confirm the performance of the proposed structure using both the numerical calculations and the experiments.
Absorption Spectra of Standard Gases for Wavelength Reference in C-band using a Supercontinuum Source Based on a Mode-locked Cr
Lee, Jong-Min ; Jeon, Min-Yong ; Ryu, Han-Young ; Suh, Ho-Suhng ;
Korean Journal of Optics and Photonics, volume 19, issue 1, 2008, Pages 54~59
DOI : 10.3807/HKH.2008.19.1.054
We report on the measurements of absorption spectra from acetylene (
) and hydrogen cyanide (
) for wavelength reference in the C-band (conventional band) region using a supercontinuum optical source generated from a mode-locked
:YAG laser. The center wavelength of the mode-locked
:YAG laser was 1510 nm and the pulse duration was 75 fs at 100 MHz repetition rate. The supercontinuum source achieved a flatness of
over a wavelength range of more than 400 nm, using a 20 m long photonic crystal fiber. The measured absorption spectra from acetylene (
) and hydrogen cyanide (
) had more than 50 lines and were analyzed for wavelength standardization.
All-Optical Gray Code to Binary Coded Decimal Converter
Jung, Young-Jin ; Park, Nam-Kyoo ; Jhon, Young-Min ; Woo, Deok-Ha ; Lee, Seok ;
Korean Journal of Optics and Photonics, volume 19, issue 1, 2008, Pages 60~67
DOI : 10.3807/HKH.2008.19.1.060
An all-optical 4-bit Gray code to binary coded decimal (BCD) converter by means of commercially available numerical analysis tool (VPI) was demonstrated, for the first time to our knowledge. Circuit design approach was modified appropriately in order to fit the electrical method on an all-optical logic circuit based on a cross gain modulation (XGM) process so that signal degradation due to the non-ideal optical logic gates can be minimized. Without regenerations, Q-factor of around 4 was obtained for the most severely degraded output bit (least significant bit-LSB) with 2.5 Gbps clean input signals having 20 dB extinction ratio. While modifying the two-level simplification method and Karnaugh map method to design a Gray code to BCD converter, a general design concept was also founded (one-level simplification) in this research, not only for the Gray code to BCD converter but also for any general applications.
Wavelength Interrogation Technique for Bragg Reflecting Strain Sensors Based on Arrayed Waveguide Grating
Seo, Jun-Kyu ; Kim, Kyung-Jo ; Oh, Min-Cheol ; Lee, Sang-Min ; Kim, Young-Jae ; Kim, Myung-Hyun ;
Korean Journal of Optics and Photonics, volume 19, issue 1, 2008, Pages 68~72
DOI : 10.3807/HKH.2008.19.1.068
Fiber-optic strain sensors based on Bragg reflection gratings produce the change of reflection spectrum when an external stress is applied on the sensor. To measure the Bragg reflection wavelength in high speed, an arrayed waveguide grating device is incorporated in this work. By monitoring the output power from each channel of the AWG, the peak wavelength corresponding to the applied strain could be obtained. To enhance the accuracy of the AWG wavelength interrogation system, a chirped fiber Bragg grating with a 3-dB bandwith of 5.4 nm is utilized. The high-speed response of the proposed system is demonstrated by measuring a fast varying strain produced by the damped oscillation of a cantilever. An oscillation frequency of 17.8 Hz and a damping time constant of 0.96 second are obtained in this measurement.
Long-Range Surface-Plasmons Excited on Double-Layered Metal Waveguides
Joo, Yang-Hyun ; Jung, Myong-Jin ; Song, Seok-Ho ;
Korean Journal of Optics and Photonics, volume 19, issue 1, 2008, Pages 73~79
DOI : 10.3807/HKH.2008.19.1.073
We propose a novel metal-waveguide structure for sustaining long-range surface-plasmon-polaritons (LRSPP). The LRSPP waveguides are composed basically of two asymmetric metal layers: a very thin, finite-width metal strip on top of a metal slab with a dielectric gap in between them. Mode cut-off of LRSPPs excited on the double-metal waveguides is characterized by consistently investigating their dispersion relations and mode profiles. We also confirm experimentally the existence of low-loss, well-confined LRSPP modes by measuring far-field outputs emerging from an edge of the asymmetric double-metal waveguides. In the experiment, we have fabricated several types of SPP waveguide devices including straight lines, S-bend, and Y-branch consisting of gold strips (20 nm-thick,
-wide). Overall propagation loss of the proposed double-metal waveguides is quite comparable to that of single metal-strip waveguides, in addition the mode sizes can be tuned by increasing the core-insulator gap between the metal layers to get a higher coupling efficiency with a single-mode fiber in telecom wavelength. The proposed LRSPP waveguides may open up realization of SPP-waveguide sensors or nonlinear SPP-devices by replacing the core-insulator with a bio-fluid or a nonlinear medium.
Calculations of the Trapping Force of Optical Tweezers using FDTD Method
Sung, Seung-Yong ; Lee, Yong-Gu ;
Korean Journal of Optics and Photonics, volume 19, issue 1, 2008, Pages 80~83
DOI : 10.3807/HKH.2008.19.1.080
Optical tweezers are a tool that can use a tightly focused laser beam to trap and manipulate micron-sized dielectric particles that are immersed in a medium with lower refractive index. In this paper, the calculation of the trapping force of optical tweezers is presented. A nonparaxial Gaussian beam is used to represent a tightly focused Gaussian beam, and the FDTD (Finite-Difference Time-Domain) method is used for computing the electromagnetic field distributions in the dielectric medium. Scattered-field formulation is used for analytical expression of the incident fields. Using the electromagnetic field distribution from FDTD simulation, the trapping force is calculated based on Maxwell's stress tensor.